water, and absorbable by porous bodies such as vegetal mould. It is, therefore, readily washed down from the air by the rain and dew, and as readily imbibed by the soil, and retained within its bosom by the peculiar physico-chemical force, already referred to as "surface-action." All fertile soils contain abundance of ammonia thus availably presented for absorption by the roots of plants. The leaves of plants also absorb ammonia from the air in quantities varying with the different genera and species.

It is not only however in the form of ammonia that atmospheric nitrogen is supplied to plants. Nitrogen combines with atmospheric oxygen to an extent always appreciable, and much augmented under certain circumstances (as, for instance, during lightning-storms), to form nitric acid; which is washed down to the soil by the rain, and assists, certainly by its solvent powers, probably also as aliment itself, in the nutrition of plants. Nitric acid also originates to some extent, as a secondary product of the decay of nitrogenous organic matters; these yielding ammonia, which oxydation converts into nitric acid and water. Furthermore, a nitrogen-compound, containing both hydrogen and oxygen, viz. nitrite of ammonium, has been lately ascertained (by Schönbein) to originate during the slow oxydation of phosphorous; two equivalents of atmospheric nitrogen taking up two equivalents of water to produce it. Nitrite of ammonium is similarly generated (according to Kolbe and Böttger) during the oxydation of hydrogen, and of hydrocarbons generally. Indeed there is fair reason to surmise that the generation of this salt accompanies all processes of slow oxydation; such as, for example, that of humus in the soil. These facts are of the deepest interest; and should the supposed universality of this natural reaction, as a concomitant of slow oxidation, be confirmed, a powerful light will be thrown on the nature and source of the nitrogenous alimentation of plants. It will indeed be a remarkable discovery, as Liebig (who cites these facts in his admirable work above mentioned*) justly observes, should it be found that the very process by which carbon is rendered available as plant-food, operates also to bring atmospheric nitrogen into a form in which it is assim lable by plants.†

This view of the origin of nitrous acid and ammonia from atmospheric nitrogen does not belong to Schönbien, but was previously enunciated by Mr. Sterry Hunt (Canadian Journal, April, 1861). See also Nickles, Silliman's Journal [2], xxxv, 263–271.

"The Natural Laws," &c., pp. 326-328, Eng. ed.

Whether free atmospheric nitrogen is assimilable by plants is a moot-point. M. G. Ville and others maintain that it is: M. Boussingault, from the results of experiments extending over twenty years, draws the opposite conclusion. Messrs. Lawes, Gilbert, and Pugh, in an elaborate paper lately published,* record the result of a series of valuable experiments on this point; and their conclusions are confirmatory of M. Boussingault's view. This therefore appears to be the opinion supported by the preponderating weight of experimental evidence; a circumstance which renders Schönbein's observation, and the conclusion to which it points, doubly interesting and important.

ATMOSPHERIC DERIVATION OF PLANTS AND HUMUS. Thus far the atmosphere, and the moisture and gases it contains, supply the food on which plants live; the soil serving merely as a sponge to bring into contact with the roots their share of this air-derived food. Even the carbon-yielding humus, though it immediately surrounds the roots, supplies them not directly, but only through the intervention of what has been above termed the underground atmosphere, by which it is slowly burned. Each successive generation of plants leaves its roots and other debris behind it; thus replenishing the soil with a fresh stock of air-derived humus, eremacausis, or decay, in its turn. Every shower washes down. nitrogen, in its acid or alkaline form, from the air; and the same cloud-supplied water furnishes the crops with their oxygen and hydrogen. It is evident that from centuries of such plant-growth as this no exhaustion of the soil would ensue.

There is certainly no result of modern investigation more calculated to strike the mind with wonder and admiration than this fact, that the mighty forests which clothe the earth, and all the vast expanse of herbage and waving crops, and all the living animals which feed on these and each other, including man himself, the lord of all, are built up, so far as concerns nineteen-twentieths of their weight, entirely of invisible gases and vapor supplied by the atmosphere.

Thus upheld, and moving with the wind, the carbon and nitrogen compounds chiefly diffused below, the watery clouds suspended above to wash them down, these, the materials of the whole organic kingdom, hover invisible around us; and by a distributive mechanism the most grand and simple that can be conceived, all

Lawes, Gilbert, and Pugh, "Phil. Trans." vol. cli, p. 431, 1861.

animated nature is wafted, as on wings, to every corner of the habitable earth. No mountain-fastness so remote, no wild so desolate, no ocean rock so lonely and so bare, but thither also float, and there descend, the viewless elements of life dissolved in air. The tiny lichen, that scarce stains the wave-worn cliff, in its wild solitude is not alone. Its food is floated to it day by day; and the same elements, sailing on the same winds, build up the delicate tissues by means of which it lives, and furnish the oxalic acid wherewith it excavates the grave that holds its dust when dead. That dust, be it remembered, is the primitive humus, and the earliest form of soil. It is derived, like the lichen itself, from the air, and it confirms the saying of Liebeg, that it is not humus which generates plants, but plants which engender humus.

(To be continued.)

ON PISCICULTURE.

The importance of the artificial breeding of fish, which the French have dignified with the name of pisciculture, is such that we have thought well to bring before our readers some of the results obtained in England and in Norway. For this we are indebted in the first place to a lecture recently delivered in London by Frank Buckland, Esq., and published in The Journal of the Society of Arts, for March 11, 1864. This lecture we have somewhat abridged. In the second place, we extract a very interesting chapter from Rev. M. R. Barnard's Sport in Norway, giving a description of the method of fish-breeding pursued in that country. Lastly, we copy from The Angler-Naturalist, an excellent book by H. C. Pennell, lately published by Van Voorst, what the author designates as Proved Facts in the History of the Salmon. -EDITORS.

ON FISH-HATCHING: BY FRANK BUCKLAND.

This is one of the most practical applications of the study of natural history that has been brought to notice of late years. The mode of hatching valuable fish, such as the trout and salmon, by artificial means, is no longer an experiment. It has, I have been pleased to see, been lately gazetted by public consent to the rank

of a science, which is every year attracting more attention. I shall not weary you by entering into the history of the art suffice it to say, that the first discoverers were two poor French fishermen, Gehin and Remi. All honor to their names for the great good they have done to their fellow-creatures.

You will find in books a statement repeated over and over again, -a fault very common in treatises on natural history,—that the Chinese were the first to practice pisciculture. But let me tell you what their pisciculture consists of. They have no idea (I have it from the best authority, viz. of officers in the army who have travelled there) of hatching fish in troughs, such as we see in European establishments, nor have they yet arrived at the practice of impregnating the eggs artificially. What they do is this: They observe the spawn of fish hanging about the bushes, having been placed there by the fish themselves. They collect this spawn, hang it up in tubs and ponds, and let it hatch out of itself. But though they have not the science that we have, yet they are pisciculturists in a most practical manner; for I have it on the authority of an eye-witness, that when the Chinese flood their paddy or rice fields with water, they turn out into those flooded fields large numbers of fish, which feed upon the worms, insects, &c., which they find in the mud, and this without injury but rather benefit to the plants themselves. When the fields have had enough water, the Chinese water-farmer opens the hatchways, catches what fish are fat enough and sends them to market; the others he lets out into another fresh-flooded paddy-field for a pasture. In fact, the Chinese herd their fish, and drive them from one pasture to another, just as a shepherd drives his sheep from one field to another. These fish are, it is said, great coarse things, and appear to be something between a chub and a tench. There are, I believe, no representatives of the Salmonidæ in China.

Leaving the history of the subject at this point, I would now proceed to the practice of the art. There may be some who say, Why not let the fish breed for themselves? Doubtless, if left alone in a perfect natural state, they would multiply themselves to an enormous extent, as is the case, I am told, at Petropaulowski, where the salmon are occasionally left high and dry by the subsiding of the floods, and such numbers of them perish in this way as to cause a plague by the putrefaction of their bodies.

When we consider the vast number of eggs which nature

has given to fish, it is a wonder, indeed, that all the world is not fish. The eggs of fish are simply the hard roe of fish; and if you examine the next red-herring for breakfast you will find that the hard roe is composed of a large number of little balls, each of which might possibly come to a fish. You will find in books on natural history the number of eggs in fish. Not trusting altogether to these statements, I have been at some considerable pains to count the eggs of the following fish. To begin with the salmon, these fish carry about 1,000 eggs to a pound of their weight; so if we can get a fish weighing twenty-five pounds, we have no less than 25,000 eggs.

If therefore a female salmon weighing 20 lbs. deposited her eggs in some safe place, and they all eventually became marketable fish, which would be in three or four years' time, we should find that the eggs of this one salmon would yield no less than 178 tons 11 cwt. of salmon fit for food; and supposing we put this down at 2s. per lb., it would be worth £40,000. Even supposing only a quarter of the young fish ever became marketable, still this one fish would yield a value of £10,000, and all without costing any human being a half-penny for food. A trout of one pound weight contains over 1000 eggs, a perch of half a pound 20,592, a smelt of two ounces 36,652, a sole of one pound 134,466, a herring of half a pound 19,840, a mackerel of one pound 86,120, and a cod of twenty pounds not less than 4,872,000 eggs, while an oyster yields about 1,500,000.

It may be asked, therefore, what becomes of all the eggs of the

The way to count the eggs is this: Make a few cuts with a knife in the membrane which contains the roe, and then plunge it into water which is, at the moment of immersion, positively at the boiling-point. Being composed of albumen, the eggs obey the natural law and coagulate in an instant. Then add a little common salt, and continue to boil the eggs till they all become quite detached from the membrane, and swim about in the water, loose like marbles. If they adhere to the membrane, they should be gently removed by a short brush, or by shaking in the boiling water. I then, when all the eggs are quite loose, draw off the water and pour the eggs into a dish, drying them slowly in the sun, or in an oven, the door of which is left open to prevent their becoming baked into lumps. I then weigh the whole mass of eggs, and put down the total weight on paper. After which I weigh out five grains of the mass, and get them counted over carefully under a magnifying hand-glass, on white paper. This is ladies' work.